1. Data Size Restriction in GET: There is a character restriction of 255 in the URL. This is mostly the old browsers restriction and new ones can handle more than that. But we can't be sure that all our visitors are using new browsers. So when we show a text area or a text box asking users to enter some data, then there will be a problem if more data is entered. This restriction is not there in POST method. We can transfer unlimited data using POST. In PHP by default 8MB of data can be transferred. (can be changed by setting the post_max_size in the php.ini file)
2. Data Type Restriction in GET: As the data transfers through address bar ( URL ) there are some restrictions in using space, some characters like ampersand ( & ) etc in the GET method of posting data. We have to take special care for encoding (while sending) and decoding (while receiving) data if such special characters are present.
3. Security: In GET method data gets transferred to the processing page in name value pairs as a query string in URL, so it is exposed and can be easily traced by visiting history pages of the browser. Data is always submitted in the form of text. So any login details with password should never be posted by using GET method. On the other hand, POST is much more secure. In case of POST, all the name value pairs are submitted in the Message Body of the request.
4. Speed: GET is faster than POST.
5. Bookmarking: There are some special cases where advantage of using GET method is, one can store the name value pairs as bookmark and directly use them by bypassing the form. But you cannot bookmark using POST method.
6. If POST method is used and if the page is refreshed it would prompt before the request is resubmitted but it would not prompt if GET method is used.
7. Uploading files through input type file is possible in POST but not with GET method.
8. There are chances for data lost after server encoding in GET method but no data loss occurs in case of POST method.
9. GET uses STACK method for passing form variables while POST method uses HEAP method for passing form variables.
10. GET can store up to 18 form variables but there is no limit in case of POST method.