That's true, but it can save you a ton of money. You just have to be aware of the risks and plan accordingly.
I have typically used this strategy when flying back to the US from the EU. Take an EZJet or similar low cost airline from random small EU city to a larger EU city like Paris, London, Frankfurt, etc... and book the return trip to the US from the larger city. I've also been forced to do this from some EU cities since there was no connecting partner with a US airline.
The difference is mind-boggling in some cases. On one trip in 2019 I had the following coach fair choices for SFO - Moscow return trip tickets booked 3 weeks prior to departure.
* UA or Lufthansa round trip (single carrier) $3K
* UA round trip SFO - Paris + Aeroflot round trip Paris - Moscow: $1K
No amount of search could reduce the gap. I went with the second option. The gap is even bigger if you have a route with multiple segments.
Yeah this strategy is good, but you need to allow a long layover like 6 hours if you have to go through immigration and change airports for the connection which happens pretty often with ryanair and ezjet. It’s a big pain, but it does save money.
If you're booking each leg with different carrier, I find it best to pay the little extra with kiwi.com and they give you guarantee for the connection. I missed connection twice and they always got me on the next flight to the destination for free.
in my ideal world the software ITA wrote for airlines and is now owned by Google would be in the hands of consumers and the airlines could have adapted to shifts in demand probably without the need for abrupt cessation of services and human fatigue on industry employees caused when route optimisation analysis tempts executives with what I suspect are ultimately fictitious net present savings.
Depending on the definition of "tight" each of us have. I remember having 40mins in Munich, and that is a BIG airport. Especially if you disembark on one side of the terminal and your flight is on the far/opposite end. That's 25-30mins brisk walking. With 5000 people in-between you could as well miss your flight. No discussion about stopping to get a coffee or a snack.. you'll miss your flight.
It doesn't really matter if it's on the same airline, it just has to be in the same reservation. Usually, that is the same thing; however on international and hyper-local (the kind that end with a Cessna) flights you'd often have several airlines with codeshares, and you could buy two separate tickets on the same airline if you wanted.
Another approach that's interesting is "buy long, fly short". Sometimes buying A->B->C and getting off at B is cheaper than just buying A->B. But, airlines can cancel the the A->B->C flight and replace it with an A->B and A->C, and place you on the A->C flight.
If you use the same airline they will make sure you get to the destination.