Most tasks can be done using the network's internet connection (3g for me) like uploading photo to facebook or downloading a new app. But sometimes I end up having to wait to find a wifi connection to say, upload a video to youtube or download a game for my Xperia Play. Why do these tasks require wifi? Are these software restrictions placed by my provider?
Most apps do this now to protect the user's mobile data usage. Knowing that most data plans are limited (200 MB a month, in the case of my roommate), developers prevent users from, say downloading a 45 MB game from the Play Store/Amazon App Store via mobile network, as this would not be beneficial, seeing as it would take almost 1/4 of your data and would take a significant amount of time and battery. Same goes with uploading.
Most apps do this as an option, though some (
NOTE: I have found that some apps that prevent Wi-Fi-less downloads (i.e. Amazon App Store) allow me to do these on my network as long as it is over 4G. If you have this option, try it and see if it works for you as well!
Most of the time it's because Battery Saver Mode is on. 3G is (often) slow compared to Wifi, so it takes a lot longer to complete large downloads and drains the battery a lot more. Turning battery saver mode off will allow you to download via 3G on many phones.
Another possible (app-specific) reason is that it just uses up too much bandwidth and wouldn't be practical on a limited-transfer 3G connection; if this is the case there's not much you can do about it.