Sharing photos and videos using Google Photos has many advantages over emailing photos.
With email, there may be size restrictions. These restrictions vary from one email server to another (such as Gmail, Yahoo, AOL, Outlook, etc, or your local internet provider's email server). Some email servers let you send and receive only 5 MB emails (the equivalent of about 5 photos when each photo is around 1 MB). Some email programs let you sent up to 10 MB emails (or 10 pictures). Others let you send 20 MB worth of photo attachments. The problem is, you never know for sure what limits your recipient will have. If you send an email with a size that the recipient's email server can't handle, the recipient will not be able to see the photos.
With email, the "payload" is generally about 1.5 times larger than the basic size of the photos. So sending a single 3.5 MB photo at full resolution COULD fail if you're sending to an email address that supports only 5 MB emails.
Because of the size restrictions of email servers, in Picasa you have the option to send smaller versions of your photos by choosing a smaller setting under Tools > Options > E-Mail tab (lower the pixels to 1600 or lower). When the size if reduced, the recipient will see smaller, lower quality versions of your photos. Before emailing smaller versions, do some experimenting using the Export button and export at a smaller pixel, so that you can see the quality of the photo you plan to email.
When emailing photos, the recipient may see a bunch of separate icons in the email and will have to click on each one separately to view the photo. Or, they may see all the photos "in line" (embedded) in the email - with a large scroll-able list of photos. Or, they may see a zip file of all of the photos. The email will not show photos as a slideshow. In the attachment area of the email, the recipient will need to click a "download zip" link to get the photos downloaded to their computer, then will need to unzip the photos. Though with some email programs such as Gmail, the recipient can easily see the photos in their browser by clicking on the photo. Downloading embedded images can be more time-consuming for the recipient (right-click the image, then "save image as"). Recipients with dial-up internet service will have a tough time viewing photos that are large.
If you use Google Photos for sharing photos, you're nearly unlimited in the size or amount of photos you want to share. You have 15 GB of free space (or whatever the current free space is at the moment). The default upload size is 1600 pixels on the long side - this will be full-screen sized on many monitors, and, in any case, much larger than most emailed photos.
Downloading your photos or movies should be easy to do (dependent upon if you have allowed downloading in your album settings). Various ways to download are described here: Downloading photos
The down-side with sharing photos via your online albums is that if you intend to take the photos offline after showing them to someone, you'll have to follow-up with the recipient to ask if they have seen your photos so that you can delete them from the online album. With emailing photos, you just send and forget it (no need to ask them if they're done looking at them).