I recently got a 3/4" 3tps blade for my old Delta/Rockwell bandsaw, but haven't done any re-sawing yet.
A guy who does a lot of resewing told me that I should not use my fence because the blade will wander with the grain. Instead, he recommends a sort of post clamped to the fence, even with the blade so I can manually correct for blade wandering by following a line marked on the edge of the board. Does that sound right to you?
I want to address @brucet999
's question: The short answer is yes and no.
Some people use the fence only like a rip fence on a table saw. They press the flat face of the board against the rip fence and push the board through the blade. That is what I do and it works well for me. The inherent assumption is that the blade doesn't drift (or the fence is adjusted for it) so that you get a reliable, straight resaw cut.
Addressing your friend's comment about the blade wandering with the grain, I have not noticed it. If it exists, it may be lost in the bandsaw saw marks that are left behind for me to plane or sand off. It may be that my experience is from resawing boards that have mostly straight even grain. I do a lot of resawing to make thinner boards for my spouse's scrollsaw projects. I just asked her, and she does not remember any resaws of very curly grain wood.
Some people do what your friend suggests, and they buy or make a curved or pointed resaw guide. It was my impression that the special resaw guides are more about compensating for blade drift rather than grain-caused blade wandering. If your blade doesn't drift, I suggest that you try resawing with the fence alone, to see what happens. I would be curious if you can see or detect wandering caused by grain.
I have a Kreg fence, and I bought the two curved resaw guides for it when I bought the fence. I tried them out, but found it was easier to control the resaw and get consistent cuts with the flat fence than the resaw guides, so they stay in the drawer for now.
There are multiple shapes for resaw guides. The Kreg resaw guides are broad curves. Some of the bandsaws at the local woodworking store have ~1 inch metal cylinder resaw guides attached to their fences. I have seen similar plastic ones, too. Some people bevel-cut two 45 degree angles on the end of a board to form a point, and clamp that to their bandsaw fence as a resaw guide.
To use those resaw guides, just attach them to the fence, and arrange it so the point or peak of the curve is just in front of the cutting edge of the blade, perhaps 1/4 inch or so. Draw the desired resaw line on the edge of the board. As you cut, keep the board against the resaw guide, but make small adjustments to the angle of the board left and right as necessary so that the cut follows the line. Smooth movement helps. Use safety protections to keep your fingers safe and out of the cut line.
If you search for YouTube videos, you will see people resawing in all different ways - some directly with the fence as I do, others with resaw guides.