Bob is right: you can use anything as a lead-on pin, including the end of the fence. Before I had a posh table I've clamped a block of wood so that the end comes close to the router spindle (2-4" away). But my current one has a mitre track, so I can still do the same thing, but clamping it on the track rather than clamps - probably more secure.
The reason for having it close to the cutter is really so that you get maximum control. There's a good argument for contriving one as/when you need to, so you can get the pivot point in the most comfortable place (as long as it can't slip - not life threatening, but usually a nasty surprise!). I'm not advocating a close-by pin because everyone else says so - but because it really is easier that way. The corner of a bit of scrap will serve, but the two points of contact - the bearing itself and the pivot - do make it much easier to keep good control.
The other thing, of course, is depth of cut: If you're using a moulding cutter with the fence, it's easy to arrange shallower passes so the final one to depth takes a minute amount of wood. The cutter is barely cutting and the result is clean (don't tell anyone, but you might even climb-cut the very last, really thin pass for smoothness).
With "freehand" moulding this is a lot harder to set up consistently, and the natural inclination of the cutter is to snatch the stock in, to full depth. There are various remedies I've seen for this, including 2-point fences (which don't use the bearing much until final depth, but need waste stock at each end of the wanted bit and a constant-radius curve), and even sticking tape round the bearing to increase its diameter (dead dodgy, IMHO). I have a really nice Wealden rebate cutter, with a selection of bearings to give different depths of rebate: a good, safe approach is to use bigger bearings to start off with and work down to the right rebate in steps.
But controlling depth of cut is a weakness of "freehand" routing, especially in natural wood rather than man-made materials. You'll probably agree the first time you suddenly hit a bit of gnarly grain in hardwood...
I've yet to need to make a sled for pattern routing, but it seems to be the most controllable approach, as you can get a good grip with both hands, well away from the sharp spinning bits.
I hope Custard is reading this, as it's the sort of thing he needs to do often (I'd guess), so he probably has a safe and good approach!).