I've been long believing that 3-pt anchor is better than other anchors, either advanced (4-pt,5-pt and 7-pt) or deep (1-pt and 2-pt), at least in the initial stages of the game. Here is my thesis:
Most of the times, BG games go such a way that one player has a lead in race and the other is following a holding/back game strategy. Of course, many times there are holding vs holding, priming vs priming and non-contact racing vs racing (and also blitzing vs dancing

situations, but as said, most of the times there is a gap in pip-count that the trailer gives up hopes for race and begins a holding/back game strategy to get a shot and turn the match.
But the important thing is that we DO NOT know from the beginning of the game that which way the game would develop. In the first stages of the game, almost everything is possible, and here's the point that I think the strenght of the 3-pt anchor comes to existence: It's a 'long term investment'. Now let me embark on comparing the advantages of 3-pt anchor over other anchors:
Advantages over the deep anchors1- If the game develops into a prime vs prime situation, there is much less chance to contain the 3-pt anchor owner, in comparison to when you have deep anchors.
2- Having the 3-pt anchor, you have more controll over the outfield and thus are more able to destroy the building plans of your opponent, as his 9-pt is in the direct range of your artillery and also you have more indirect shots.
3- Having the 3-pt anchor, you will have a chance to even hit your opponent's running men even in your own outfiled: with a 6-5 on your 14-pt.
4- If you roll a double 6s or double 4s, you will have a much better chance to turn the course of the game into an effective racing vs racing state than having a deep anchor.
5- with a double 6s, you can build a valuable outfield pt in your 10-pt, while with deep anchors you can't.
Advantages over the advanced anchors1- If the games goes in such a way that you're well behind in the race, it's usually much better to have a deep anchor as your chances to get a shot is higher. If you have an advanced anchor, your opponent will have a much easier bear-in, because he simply can get his men jump over your anchor into his home. 3-pt is not as deep as 1-pt and 2-pt anchors, but it's not advanced too and it's almost very difficult for your opponent to jump over your anchor.
2- If you'd like to follow a backgame strategy, having a 3-pt anchor is almost always neseccary. With 3-pt anchor, every other anchor makes an exellent backgame (exept for with 5-pt perhaps), but out of the 3 advanced anchors, just the 4-pt anchor can be used effectively to follow a backgame strategy and the others are almost useless.
3- If your opponent was not able to make his 7,5 and 4 pts, then he will have tough problems in bear-in stage, because he must choose between two things: either burry checkers in 1 and 2 pts, or stack them on 8 and 6 pt (or buliding pts in outfield), which both of them will harm his effective pip-count and might prove fatal if the 3-pt anchor owner rolls a big double. But with an advanced anchor, especially 5 and 7-pt anchors, the race leader will have much less troubles in making a nice board that wil pay-off in the bear-off stage.
ConclusionHaving the 3-pt anchor will serve it's owner, in almost ALL kinds of situations, though in NONE of the it's the best, but it's the ONLY anchor that has such wide-spread usage in all kinds of situations.
Now, please let me know, are these reasons just wrong illusions of an intermediate or not.
Thanks