Frankly speaking, A lot !

I have been travelling daily by Mumbai local trains almost for 4 years till now (ie: till the date of writing this answer).

Firstly, If you live in Mumbai or its suburban areas then there is no other cheaper option and faster way to travel in this city than by using Mumbai's very own lifeline - The Mumbai local.

Mumbai local travel teaches you many things in due course of your commute including sharing,respect,compassion,empathy,brotherhood and more importantly adjustment.

It teaches you how to adjust with your fellow passengers irrespective of their age,creed,religion,etc. Especially,during rush hours when you have no other option than to adjust yourself for others.

It also taught me how to share the seat.If you have travelled from Mumbai CSMT to Kalyan/Karjat/Kasara or vice versa you would know what I have to say.You have to give the standing person your seat(if you have been seating till now in the commute) at THANE station.Though, it is a not written anywhere but most of the commuters who travel such distances daily follow it (especially,in general compartments). It surely provides relief to the other standing persons, especially to their legs.Moreover, you would also receive the reward of this good deed if you find yourself amongst the standees one day.

It also taught me how to adjust my backpack during my jam-packed commute.Since, I travel in the morning rush hour and stand at the doors (most of the times).I learned this technique (after travelling through a couple of trips in mumbai local) to keep my bag in between my legs so that it would help others commuters in terms of creating space for them while getting inside the train or during commute,etc.

I learned this thing during my commute in Mumbai local trains, that we should care for humans first, before other non-living/man-made things.

Also, I got to know more about how Indian railways work,their signalling,their services,etc by travelling daily through Mumbai local trains.That thing also invoked my inner self and guess what I got a new hobby or say passion of railfanning.

So,at the end of this answer I would like to say happy travelling and happy commuting through Mumbai local trains. ;)