No, it is necessary only for Presto shops that require you to enter the shop while at the location. You can, and I have, submitted Presto shops on my computer. Of course, you would need to install the Presto app on your computer first.
A lot of Presto shops require a geolocation code, and some won't allow you to open the survey unless the app thinks you are at or near the location. But if you pick up a shop and then can't complete it, there's no penalty, so if you see a shop you want give it a try.
The Presto Instashops with the "I" teardrop icon have to be done on the app on a smart device while you're on location. You can't start the shop until the app verifies your location. But, even the largest smart phone is too small to make sure I get all of the correct information and pictures into the reports. So I bought myself a 10" tablet, it does everything my smart phone does, it takes pictures, all of the apps from the google play store work on it, and I can SEE everything, even the thumbnail photos are large enough to tell which ones I'm uploading. The only thing it doesn't do is make phone calls, so my son can't call me in the middle of a shop and mess up an upload..
I have only done one Presto shop and it was about a month ago. It did need geolocation to open the rest of the form to me. For whatever reason my phone told them I was somewhere 100's of miles away. After rebooting a few times this never changed but a question popped up that asked if the geolocation was incorrect. After I checked yes it allowed the shop to continue.
You can open the report anywhere, and it says you are X miles away. For example, when I sign up for the green gas stations, which are usually far I always check in on my computer, at home, click on yes to populate the full report. When I go to the location I open the report on my cell phone and click on the reverify location and then it says we find you are close enough, thank you.