Analogy here is somewhat like coke and water, good to have both. But there's always one better depending on the situation. I for one would like the best of both worlds so I invest in both alt coins and bitcoins. Both side of the cryptocurrency coin is best when you have both at your disposal.
Good analogy. Anyone who is interested in a similar question, I advise you to study the technical documentation of Bitcoin and the Altcoins of interest, you will immediately understand the difference between the projects, how they differ and what are the advantages of each.