The big problem with Long-Term Investment is that by the time you can actually take credits of it it will have twice as much credits on it as its trash cost. Even if you do immediately empty it upon hitting 8 the previous runner's turn it will have 6 on it, making it an obvious target for the runner.
So you need to protect your investment, or use it to somehow lure the runner into something like a Prisec.
Compared to the plain old PAD Campaigns a Long-Term Investment is much more risky since it has a payout (which also costs a click) one every four turns while PAD Campaigns pay every turn so if the runner trashes a PAD Campaign that only affects non-accrued income. On the bright side Long-Term Investments do generate twice as much income as PAD Campaigns.
I guess in NBN: Controlling the Message and perhaps even in Gagarin Deep Space: Expanding the Horizon Long-Term Investment can work. Especially in CtM the extra trash cost is interesting. However CtM decks typically pack the even more efficient Commercial Bankers Group so Long-Term Investment doesn't really add much for them. On the other hand with the CtM staple Sensie Actors Union now costing 3 influence some CtM decks may be in need of money that's influence-free.