https://sheldonbrown.com/brandt/presta-schrader.html

In the past, sports and racing bicycles used Presta valves because they are slender and enabled racers to inflate tires with a simple pump with attached chuck (pump head) and no hose. Presta valves are easier to pump than Schrader, because they have no valve spring to overcome. Although a valve depressor for Schrader valves can alleviate this, it requires a check valve, impractical to house in lightweight pump heads.

The small diameter of the Presta valve requires a smaller hole in the rim, whose size is important for narrow rims where cross sectional strength of is significantly reduced by a stem hole. In narrow rims, clincher tires also leave insufficient space between tire beads for larger Schrader valves.

casual rider ? drill the hole out and replace it with Schrader tubes, or just carry an adaptor, they screw on, use then screw off.

i assume it has tubes though ?

very narrow rims on road bikes mainly

mine are all presta

For casual riding there's no benefit to a presta valve over schrader. If he were using the bike for heavy intensity MTB, the only benefit would be a smaller valve hole in the rim, creating a stronger hoop.

If the rim is wide enough, you can simply drill the valve hole open and use a schrader valve, assuming he's got a rim diameter that schrader tubes are made for.

There are none in my opinion

It's marginally easier to let air out the tire with a Presta valve which is handy if you're a mountain biker who likes to mess with tire pressures.

I'm a mountain biker who likes to mess with tire pressures and I've drilled all my rims and use Schrader valves instead as needing a tool to let out some air is a fair trade-off considering it's a superior valve in every other way.

The main one for me is: when running low tire pressure on my 26er mtb, I had more than a few incidents where the Shrader valve got pulled into the rim or the side was cut by it. Presta is not necessary for casual.

My favorite thing about Presta valves is that you can remove the cores, and swap in Clik valves. Those are better than either Presta or Schrader with the minor downside that it's even harder to find a pump that fits.

Presta valve cores are removable, so you can remove the core to put sealant in through the valve without unseating the tire bead, and can connect a pump to the valve stem without the core in to inflate quickly to seat tire beads on diffucult-to-seat tires/rims.