Not all travellers are made equal when it comes to long distance travel. If you are travelling at a moderate speed, with a caravan, on roads within the consensus then you are unlikely to suffer any penalties. However, once you are attempting to get somewhere quickly, are suffering from interrupted sleep within the flux, and are spending everyday covering difficult terrain this is unlikely to still be the case. Some characters will have skills which negate these penalties for themselves, some characters will have skills which lessen these penalties for everyone.
Forced march occurs when you have to reach a location quickly, where the loss of a day could be a big deal. It involves a constant rotation of walking at a rate faster than most adventurers will be used to for 3 hours at a time, with either very short food and rest breaks or 6 hours of sleep.
In this circumstance most characters can expect to lose access to both dodges and body hits. This can be lessened by choosing not to wear armour while travelling, by a wayfinder selecting more beneficial terrain, and with the aid of a survivalist. Only characters with specific relevant skills will be able to completely negate penalties in this circumstance.
There are numerous situations where a character may choose to skip a nights sleep. This increases the likelihood of becoming addicted to alchemy as covered in the addiction rules, and will probably result in loss of dodges with no sleep at all or regularly sleeping for only short periods.
When travelling at a sensible rate, but for an extended time, it is likely that less seasoned travellers will start to suffer. This will usually result in lost body hits, and can be treated by medics, eased by survivalists and wayfinders, and negated with appropriate personal skills.