I don't think just tethering is what pang was talking about. If you do PC-Suite mode and select mobile broadband, you can't ssh from the pc to the phone. Your PC and your N900 actually get assigned different IP addresses from your mobile provider, The PC just treats the n900 like a modem.

With MobileHotSpot, the n900 connects to the internet, and then uses NAT and DHCP. The n900 is assigned the address 10.241.231.1, and your PC is 10.241.231.10.
I think this is what Pang was talking about. In this case, the tethering is just a convenient side-effect.

As an added bonus, back on the n900 you can disconnect from your mobile ISP, and then connect to a WiFi AP, and the n900 will tether your PC to the wifi. This is very convenient for me, as the range on my laptop's internal wifi card is terrible, and with this technique I can extend my laptop's wireless range as well.

Also, tethering with mobilehotspot works much better. When you tether with just PC-Suite mode, the PC and the N900 don't like to send/recieve data simultaneously. Internet usage on the N900 will drop your PC's connections, because the PC just sees the n900 as a modem. With MobileHotSpot, ONLY the n900 connects directly to the internet, so simultaneous connections aren't a problem.