I have a 2.5yr DS and a 1year old DD and expecting my 3rd in April next year. Yes they were all planned as I am often asked.
The biggest pros and cons for me having my kids so close together were;

pros:
1. The biggest pro was my #1 was still on 2 naps aday (he was 15mths) when I had #2 so it was much easier for me to nap or just lay down whilst the newborn just played on her back or had a nap herself.
2. #1 was more excepting of my laying on the couch while he played when pregnant wth #2. Now he is 2.5yrs and I am doing the same as I am preg with no.3 , he gets annoyed with me and misbehaves but #2 doesnt care what I do as long as she can see me - she is only 1yr old.
3. Being only 15mths apart they both often join in and enjoy the same sorts of activities which is easier on me.
4. They both go to playgroup together.
5. The thing I thought about the most is that they will all go to school 1 after the other and it will be easier to do stuff with them when they are all older because they will be close in age. A lady at my work told me that is the biggest issue for her. Her girls are 6years apart so going on family trips is hard because they have to cater activities for a teenager and a little girl.

cons:
1. Still having to pick up #1 when heavily pregnant with #2. SO having the same issue again now preg with #3. Both #1 and 2 are too small to get on their seats by themselves.
2. The first few months were hard with my second. Often I would be feeding #1 breakfast whilst breastfeeding #2. My first couldnt feed himself yet.
3. If you go out alot you need a double pram and they can be heavy and annoying and take up all my boot space!! A double stroller wont work if it doesnt recline for the newborn.
4. I thought I was ready to have another so got pregnant when #1 was 6mths. Mentally I was ready my for me it turned out that my body was not quite ready and my 2nd pregnancy was harder physically.


Hope this helps. Good luck