Some people do a lot of things. I have found that it is really not necessary.
If you were using a short ester like prop of test base, then it would be necessary to taper down so that your levels do not crash overnight. The difference in a half life of 7 days and a half life of 7 hours is a big thing.
If you were doing test base at 75mg every day, drop it to 50mg for three days, then 25, for a week or so, while starting your clomid and nolvadex while you are dosing at 25mg a day.
If you think about the timing of pct on a Test E cycle, it's two weeks after your last shot. If the half life of test e is 7 days, and you are doing 500mg a week, you still have 125mg of exogenous test floating in your system when you start post cycle therapy (pct). Dosing test base at 25mg a day, you will also have around 125mg of test in your system.