Society makes you think that when you have a child you first need to have a bassinet for them, then a crib, then a toddler bed, then a full or twin bed. Wow, that is a lot of furniture, and A LOT of money! Here in my household we have a much different opinion. When our son was born we had a very very tiny one bedroom, so of course he slept in our room. We had a crib only because it was a family crib of my in-laws that they let us use. When we moved and our son outgrew his crib we started looking around for a bed. Both my husband and I saw no use in a toddler bed because when he outgrew that we'd have to buy yet another bed. We knew we wanted more children so we decided the best route to go was to get a bunk bed. Best decision ever!!
Our son can use this bed well into his teenage years, and then we have an extra bed for guests. Because we didn't have a lot of storage space we decided to completely set up the bunk bed, but instead of setting up two beds, we use the top bunk as a loft for our son to play with his cars and toy trains. He loves to climb up there to play and it saves on floor space. My husband just cut out a piece of plywood the size of the bed, then covered it with some old carpet. Very stable (even for me) and lots of fun for our son and his friends.
So, if you're deciding on whether or not to get a toddler bed.....I say no! Go the bunk bed route and save some money in the long run!
P.S. The only advice I'd give in buying bunk beds is to buy really good quality, sturdy ones, even though they will be quite a bit more it makes all the difference in the world! We didn't have a lot of money at the time, so we just bought this set form Walmart. We've moved a few times since then and they have gotten pretty banged up. I really wish we would have bought the set that Deseret Industries sells (in their line of brand new furniture).