Does Google Backup and Sync replace Google Drive and Photos?

Yes, you don't need Google Drive and Photos on your computer anymore. However, my suggestion would be to continue using both these products till Google Backup and Sync (B&S) is rid of a sync related bug, or till support is withdrawn (no more updates after Dec 11, 2017; blocked after Mar, 2018). The bug results in repeated attempts at synchronizing local folders with Google Photos.

If you would still like to install it, go to Settings in Google Photos and note folders that are being synchronized with the Google Photos site. Then, uninstall Photos and install B&S. Google Drive would be uninstalled automatically. You'll be asked to restart the machine.

After the restart, open B&S from the tray and select Preferences from the menu which would display the following screen:

Google Backup and Sync: Preferences screen

Set the options for Size and Removing Items as shown above. The setting shown will preserve your photo on the Google Photos website even if you delete it from your hard drive (this was how the old Google Photos app worked). Conversely, this setting does not sync your Drive if you delete a file locally (this behaviour is different from the earlier Drive app; if this option is important for you, please see the comments in this blog post; in short, there is no other way till Google B&S is updated).

Then, select Choose Folder and add the folders that must be synced with Google Photos (which you have noted down). This won't duplicate photos if the folder has already been uploaded by Google Photos. However, B&S would again go through the folder contents and compare it with what's present in the Google Photos site to ensure all is well.

Certain file types may not have been uploaded by Google Photos e.g. TIF, THM. However, B&S uploads files of these types too. Thumbnail related files like thumbs.db and zbthumbnail.info would also be uploaded by B&S. As of now, there is no setting for what files must be synced.

Select the checkbox labeled "Upload newly added photos" if you would like to keep the folders synchronized with the Google Photos site in future.

Google drive: backup and share documents privately

Think of Google Drive as your hard disk/drive on the internet (your private space on Google's hard disk on their server). With a Google login, and the Google Drive software installed on your device, you can do the following:

• Save/backup files on the cloud and access from anywhere - 15GB drive space is free across Drive, Gmail and other Google products.
• Share the files with privacy/security.
• Files can even be edited simultaneously by yourself and and your collaborators.
• Files can be easily attached to mails if you use GMail.

Buy additional space when you need. Hardware keeps getting cheaper while the size of hard disks has been going up. So the cost of space you own keeps goes down.

Important features for sharing

• File could be shared by specifying the e-mail addresses of those with whom you wish to share (recipients)
• Specifying e-mail address is a better option than using links to share files. 
• Private sharing is possible only if the recipient is on Google+.
• Recipients can be permitted to just view files, or even edit files. 
• The feature to download a shared file can be disabled. 
• A shared file cannot be downloaded by those who can only view that file. 
• Those who are permitted to edit a file can also download it. Use the check box in the details section of the file to prevent download. 
• If you install Google Drive on your device, selected folders on it could be synchronized with the cloud drive (on Windows, right click on the Google drive icon in the notification area at the bottom right). An example usage scenario is when you would like to back up everything to Google Drive, but wouldn't want to retain all of these on the laptop as the space available is limited. 
• Upto 15GB is free. $2 upto 100GB. $10 upto 1TB - see this for how prices have declined over the years. 

Other options

• Apple iCloud, Microsoft OneDrive and Amazon's Cloud Drive are alternatives. 

Photos and video

• Photos and video shot with devices from Apple, Microsoft, Amazon can be stored for free in their respective cloud drives. For Android phones, storage for photos and video is virtually unlimited on Google Photos.
• Subscription to Amazon Prime gives you unlimited storage for photos. If you don't get Amazon Prime or an Amazon device, its cloud storage is expensive.

My readers and I would like to hear your experience in sharing documents, photos and video via the cloud.