If you are receiving VFR flight following, is it necessary to contact approach control when entering Class B or Class C airspace when you are planning to transit through the airspace?
Yes. If center doesn’t hand you off, it’s your responsibility to be sure you are in touch with the approach controller before entering B or C airspace.
For C, you have to be identified by tail number before entering.
For B, you must be cleared to enter Bravo. Tail number identification is not enough for entry into Bravo, you must be cleared.
Hope this helps.
Allen
Thanks Allen. I knew the procedures for entry into the airspace but not when transiting through. I appreciate the quick response.
Been a looooong time since I have used VFR flight following since getting my instrument rating, but generally center will hand you off well before getting to B and C airspace, so more often then not, the transition will be “transparent” so to speak, but if you find yourself closing in on that airspace and center has not handed you off, then you should query center.
If you are high enough, it’s possible that you won’t even transition C airspace and you don’t need to talk to approach controllers, though it would be prudent to be in touch if nothing else to be aware of traffic popping out of that airspace.
Of course, to transition the airspace, you do have to enter it. 
thus me putting in the entry requirements.
Allen
Well, Hopefully in about 10 more hours, I’ll have my instrument rating and this won’t be a problem. You do get spoiled not having to do it the “old fashioned” way though.
Alan
10 hours left? Sounds like you have the worst behind you as by this time, you should have hold entries down, hopefully your loooooong XC down and now it’s hopefully just a matter of polishing up your newly learned AND earned skills
Basically only not so transparent airspace is MOAs and restricted areas, everything else you are cleared through which is the beauty of the IFR. It’s a given of course to avoid P40 under any rule
Allen
It is worth noting that flight following is available based on traffic loads, and with that you will notice when it is busy around that class B, you will not be cleared to enter. I have probably transitioned 50 times around msp, and maybe been denied 5 times. It is also useful on occasion to transition class D airports, and that little trick saves me around ten minutes per trip. Never been denied on that one.
Just curious, Delta airspace takes very little real estate going up to generally 2500 over the surface of the airport and generally small in circumference.
How would going around that kind of airspace save you 10 minutes when it’s just so easy to go over the top or around???
Don’t get me wrong, I am all for talking to ATC, but 10 minutes saved per trip seems a mite large just dodging delta airspace???
Allen
I’m based at Class D airport under a Class B shelf and I use FF quite often (no IR yet). When I get 20 miles from the Class B - I get a hand off from the neighboring facility and the DFW controller normally clears me into the Bravo airspace after I check in. Sometimes they delay my clearance for a few minutes and in a couple of high traffic occasions I’m denied access. But I always get a separate clearance into the Bravo and if I don’t hear it, I ask.
Mike