The questions are as comical as it sounds, but happens all the time. Another guitar? How many does that make now? At one time, the answer for me was...14 if I remember right... Yes, you can laugh. But this question has caused stress in many relationships and ridicule towards musicians. But please... let me try to explain, for all guitarists out there with partners not understanding the reasoning... I will do my best to assist, but will not be responsible for your relationship status or bank account balance as a result.
Reason #1: The PRIMARY reason I started building on more than more bass guitar: Always carry 2 on stage. Because, strings break, electronics go stupid, things happen. And yes... I've broken a bass string. backup bass on strings older than my socks... but yes... I still broke a string... and so can you! Whether you got a twenty minute gig or a five hour night, if anything goes wrong, you're going to have a hard time under the clock to repair your equipment, and get the entertainment back on track. Or become the entertainment, choice is yours I guess...
Reason #2: Tone. Different guitars have a lot of variations. Type of wood. Pickups. the electronics to amplify the sound. Even the type of strings can change the true sound a guitar can make, before it hits the effects pedals. To attempt to clarify how much a difference that could make, brown sugar or white sugar in your baking? 5w30 or 10w40 oil in your car? Coke or Coke Zero? Does it really matter? If you say no, leave my cookies, my Jeep, and my sodas alone please, thanks.
Reason #3: Tuning. As a songwriter, some songs I wrote in standard tuning, some songs were in dropped tuning. I've seen musicians tune their guitars a certain fashion simply because the original was played that way. Keith Richards Only uses 5 strings on his guitars, tuned G, D, G, B, D. Jimi Hendrix tuned his guitar as Eb, Ab, Db, Gb, Bb, and Eb.
Reason #4: Acoustic vs Electric. The sound of an acoustic guitar recorded on a microphone sounds TOTALLY different than an acoustic electric being plugged into the mix. There's something about the way an instrument is recorded that a digital interface just can't duplicate.
Reason #5: We're musicians. we're particular in our sound, and the way we deliver it. We may have to ask you three times what you just said from the other room, but we WILL notice the sound on that Gibson just isn't as crisp as the tone ESP can provide. It will not sound right. If you ask my Gibson crazed guitarist buddy...he'll tell you the opposite. My blog, not his.
In the end, yes, a lot of the reasons have to do with sound. There's also playing comfort, and situational preference. Some women feel the shoes are ideal for the situation, some guys feel the motors are best suited for the track, the musicians will determine the best instrument for playing the song. Now if you'll excuse me, I need to browse through Guitar Center... stay creative!