Pro: You get to go back to your home town after training and resume “normal” life. You may also split Basic/Advanced training so you’re back home even sooner. Plus while on drill/training duty you may be involved in community-oriented projects.
Con: For 8 years, you are subject to being mobilized and deployed on short notice all the way to Yagottabejokinstan, and the deployment can be extended, thus seriously interrupting “normal life”. And the Reserves are now to be used as a matter of course in any major sustained operations.
Pro: Not all deployments are to Yagottabejokinstan, and you may actually be doing something like building childrens’ hospitals in some lush tropical island.
Con: Or, elsewhere in Yagottabejokinstan. Pack flea powder.
Pro: You’re still serving your country and expressing a willingness to put your arse on the line if called upon, which more than the bulk of the population can be bothered with.
Con: That “putting your arse on the line” bit. While activated, people may try to kill you violently, and the pay is NOT impressive for something that involves being shot at. And since you train with deadly devices, accidents happen.
Pro: You may be eligible for tech training, specialty bonuses, and education aid.
Con: Your choice of training and specialty is limited to those billets available at a unit where you’re able and willing to get to on a regular basis.
Pro: You can accrue Veterans benefits and a pension.
Con: You don’t get these until after satisfactory completion of service, and in the case of the pension, not only do you have to be in 20 years and get a smaller one (having been a part-timer), you have to wait 'til you reach civilian “retirement age” to start collecting.
Con: Depending on your unit/specialty, you may be stuck for long times at a lower rank.
Pro: However this means you can stay for a longer time doing what is your real job, rather than be “promoted” into staff billets you don’t care for.
If your physical condition absolutely precludes running >a half mile a day, you may have trouble. The “lightest” services require you to be able to complete a 1.5 mile run in a fixed period of time before the end of Basic Training. OTOH if a physical condition is such that it can be corrected thru treatment or training, and you can be get yourself to the point they consider that you can stand their training, they may have a look at you.